CN112005109B - Apparatus for quality determination, tank apparatus - Google Patents

Abstract

The invention relates to a device (9) for determining the quality of a liquid, in particular an exhaust gas aftertreatment agent, having at least one inspection unit (7) which can be arranged in a tank (2) for storing the liquid, comprising: at least one ultrasonic transducer (10) for transmitting and receiving ultrasonic signals; and at least two ultrasound reflector surfaces (11, 12, 14) for reflecting the transmitted ultrasound signals back to the at least one ultrasound transducer (10), characterized in that the at least two ultrasound reflector surfaces (11, 12, 14) are directly configured or arranged at different distances from the ultrasound transducer (10) on a common and one-piece carrier element (13).

Description

Equipment for quality determination, box equipment

Technical Field

The present invention relates to a device for determining the quality of a liquid, in particular an exhaust gas aftertreatment agent, the device comprising at least one inspection unit which can be arranged in a tank for storing the liquid, the inspection unit comprising: at least one ultrasonic transducer for transmitting and receiving ultrasonic signals; and at least two ultrasonic reflector surfaces for reflecting the transmitted ultrasonic signals back to the at least one ultrasonic transducer.

The invention further relates to a tank device, in particular a reducing agent tank device for an exhaust gas aftertreatment system of a motor vehicle, comprising a tank for storing and providing a liquid, in particular an exhaust gas aftertreatment agent, and a device for determining the quality of the liquid, wherein the device comprises at least one testing unit arranged in the tank.

Background technique

Devices and tank devices of the type mentioned at the outset are known from the prior art. In order to meet increasingly stringent regulations on exhaust emissions of motor vehicles with internal combustion engines, it is necessary to reduce nitrogen oxides (NOx) in the exhaust gas, especially in diesel engines. For this purpose, exhaust gas aftertreatment systems are used, which selectively reduce nitrogen oxides to nitrogen with the aid of aqueous ammonia. In particular, the so-called selective catalytic reduction (SCR) has proven to be particularly effective here. In this case, an aqueous urea solution is used as a reducing agent, which is introduced into the exhaust gas duct upstream of the SCR catalyst. The urea solution forms ammonia upstream of the catalyst and/or in the catalyst, which ultimately achieves the desired reduction of nitrogen oxides in the exhaust gas with the aid of the SCR catalyst.

In order to ensure reliable operation of the exhaust gas aftertreatment device, the reducing agent can be provided in the tank in sufficient quantity and quality. In the case of too low a quality, in particular due to too low a concentration of reducing agent in the liquid, the efficiency of the exhaust gas aftertreatment system is significantly reduced. In the case of too high a urea content or too high a urea concentration, the excess ammonia formed does not react with the nitrogen oxides in the exhaust gas and is emitted. It is therefore very important to be able to monitor the quality or concentration of the reducing agent, in particular the quality or concentration of the urea content in the reducing agent, and also to sense the impermissible replenishment of the tank with water instead of reducing agent.

A variety of different devices for monitoring the quality or concentration of reducing agents by ultrasonic signals without contact are known from the prior art. Therefore, for example, the public text US2016/041024 discloses a device of the above type. The device has a piezoelectric acoustic transducer as an ultrasonic transducer, which is a transmitter and a receiver at the same time. The ultrasonic transducer first sends an ultrasonic signal to the liquid in the tank, wherein the ultrasonic signal is reflected back to the ultrasonic transducer by an ultrasonic reflector and enters the liquid again. The propagation time measured between sending and receiving of the ultrasonic signal and the assumed known propagation path length are used to identify the liquid sound velocity and thus the concentration of the reducing agent in the liquid. However, due to the change of the materials used in the system, which is temperature-related, mechanically-related and aging-related, the actual measurement path may change, and thus the measurement result may change. In order to consider this change, it is proposed in the public text DE10 2015 212 622A1 that the thermal deformation of the reflector is physically modeled, and the propagation time measured is considered by means of a correction factor related to temperature when analyzing and evaluating the propagation time.

In addition, it is known from the publication DE 10 2013 219 643 A1 to provide two reflectors to reduce changes in the measuring path due to heat and aging, which have a negative impact on the accuracy of the inspection unit. Here, the reflectors are each constructed as a reflector cylinder, the outer circumference of which constitutes a reflector surface, so that the corresponding reflector surface is arranged on an independent carrier element, wherein the reflector cylinder is fastened or held on an independent base plate. In addition, the concentration determination is not based on the propagation time measurement of the ultrasonic signal, but on the evaluation of the propagation time difference measured between two reflector cylinders arranged at different distances from the transducer. Another device for quality determination is also known from the publication DE 10 2011 086 774 A1, wherein the reflector is arranged at an angle relative to the sound wave transducer.

Summary of the invention

The device of the present invention has the following advantages: it can be manufactured at low cost and the measuring accuracy of the inspection device is significantly improved. By the advantageous arrangement and configuration of at least two reflector surfaces, the measuring accuracy is optimized and, in particular, accurate measuring results can be provided even when the temperature in the measuring medium and/or the ambient temperature changes. Here, the mechanical stresses that may be generated due to manufacturing tolerances and/or assembly tolerances and aging effects determined by the material are also taken into account by the advantageous device. Here, the present invention is based on the following concept: two sound propagation paths are used, which have a propagation path difference between the two paths that is known due to the reflector geometry. According to the present invention, for this purpose, the inspection unit has at least two ultrasonic reflector surfaces, which are directly constructed or arranged on a common and one-piece carrier element in a manner of different distances from the ultrasonic transducer. Therefore, the reflector unit or reflector component composed of the carrier element and at least two ultrasonic reflector surfaces is a structural unit in which the arrangement of the reflector surfaces relative to each other has been predetermined during manufacturing or pre-assembly outside the box. Due to the one-piece carrier element, different thermal expansion coefficients have no effect or only a minor effect when measuring the propagation time difference of the ultrasonic signal. The material of the carrier element is preferably selected so that the carrier element has the smallest possible thermal expansion within the set temperature range. The remaining influence of thermal expansion can be systematically corrected by an advantageous structure. By preferably using the differential measurement principle, the influence of position tolerance or orientation tolerance during assembly is further minimized. The absolute spacing between the ultrasonic transducer and the corresponding ultrasonic reflector surface is not included in the calculation of the propagation velocity, so it does not have to be known and does not have to be constant within the scope of application. The real measuring section is determined only by the reflector component of the carrier element with a one-piece structure. The carrier element is manufactured, for example, by a low-cost manufacturing method, such as a stamping method or a modification method or an extrusion method. Thus, low-cost manufacturing can also be achieved in large-scale manufacturing. The construction of the reflector component is not limited to the presence of two ultrasonic reflector surfaces, but more than two ultrasonic reflector surfaces can also be constructed or arranged on the carrier element.

According to a preferred embodiment of the invention, the ultrasonic reflector surface is designed to reflect the ultrasonic signal directly back to the ultrasonic transducer. This means that the ultrasonic reflector surface is arranged opposite the ultrasonic transducer to ensure direct reflection. This results in a particularly simple structure of the inspection unit, in which the propagation time differences to be sensed are directly obtained from the distance of the ultrasonic reflector surfaces relative to each other in the direction toward the ultrasonic transducer.

According to another embodiment of the present invention, it is preferably provided that at least one of these ultrasonic reflector surfaces is configured to be used for the ultrasonic signal to be deflected at least once before it is reflected back to the ultrasonic transducer. In this case, the ultrasonic signal is therefore not directly reflected back to the ultrasonic transducer by at least one of these ultrasonic reflector surfaces, but is first deflected or reflected to at least one other reflector surface, in particular at least one other ultrasonic reflector, from which the ultrasonic signal is deflected back or reflected back to the ultrasonic transducer. By multiple deflections, the propagation time difference of the ultrasonic signal reflected back is increased. The propagation time difference of the two reflected ultrasonic signals must be at least so large that the two ultrasonic signals can be clearly separated from each other in time. In addition, due to the longer propagation path difference, the longer propagation time difference also improves the accuracy of the medium characterization. By the above-mentioned advantageous construction, the propagation path difference is increased in a simple manner. It is currently believed that two ultrasonic signals are reflected back to the ultrasonic transducer, but more than two ultrasonic signals can also be reflected back, for example, in a manner that at least three or more ultrasonic reflectors are opposite to the ultrasonic transducer and the transmitted ultrasonic signal is directly or indirectly reflected back to the ultrasonic transducer in different ways.

According to a preferred configuration of the present invention, at least one of the reflector surfaces has a curvature or is curved, in particular, is concave or convex. As a result, the signal-to-noise ratio of the ultrasonic signal is improved. Sound field focusing can also be achieved based on the curvature of the ultrasonic reflector surface. For this purpose, the relevant ultrasonic reflector surface is shaped, for example, in the shape of a parabola, a spherical shell segment or a cylindrical shell segment.

Furthermore, at least one of the reflector surfaces is preferably arranged next to the ultrasonic transducer and offset relative to the ultrasonic transducer in the propagation direction of the ultrasonic signal and opposite to another of the ultrasonic reflector surfaces. Thus, one of the ultrasonic reflector surfaces is located next to the ultrasonic transducer, but offset relative to the ultrasonic transducer in the propagation direction, so that the signal does not have the same propagation time between the two ultrasonic reflector surfaces on the one hand, and does not have the same propagation time between the ultrasonic transducer and the other ultrasonic reflector surface on the other hand, so that the received ultrasonic signal can be clearly evaluated and multiple reflections can be separated from each other in particular. One of the ultrasonic transducers reflects the sensed signal back to the other ultrasonic transducer, which then reflects the multiply reflected ultrasonic signal to the ultrasonic transducer. As a result, a particularly large propagation time difference between the two ultrasonic signals sensed by the ultrasonic transducers is obtained.

In addition, preferably, one or the other ultrasonic reflector surface has a curved reflector surface, and in particular, the other or one ultrasonic reflector surface has a straight or flat surface. Here, the curvature is selected in particular in relation to whether the ultrasonic transducer sends divergent ultrasonic waves or plane waves. If the ultrasonic transducer sends divergent waves as ultrasonic signals, the opposing ultrasonic reflector surfaces are preferably constructed to be curved so that the reflected ultrasonic waves are planar. This achieves that a portion of the reflected ultrasonic signal reaches the ultrasonic transducer, while another portion reaches the ultrasonic reflector located next to it. The portion that reaches the ultrasonic transducer is detected as a first echo. The other portion is reflected back on the ultrasonic reflector surface opposite to the ultrasonic transducer, where it reaches the curved reflector surface again and is deflected back to the ultrasonic transducer when reflected again, where the other portion is received as a second echo. However, if the ultrasonic transducer emits a plane wave as an ultrasonic signal, the ultrasonic reflector opposite the ultrasonic transducer is expediently designed to be curved or flat so that the reflected ultrasonic signal or the reflected wave is curved and thus reaches both the ultrasonic transducer and the ultrasonic reflector located next to it.

Furthermore, it is preferably provided that the carrier element has at least one notch in the reflector-free region. This reduces the weight of the carrier element and also reduces the number of surfaces capable of reflecting ultrasonic signals. This advantageously reduces interfering signals and signal noise.

According to a preferred extension of the present invention, at least one of the ultrasonic reflector surfaces is configured as a coating on a carrier element. This ensures that each ultrasonic reflector surface is particularly simple and precisely positioned on the carrier element. It is preferred that metal, ceramic or other materials with high acoustic impedance are used as materials for the corresponding ultrasonic reflectors. In the case of using corrosive media/liquids, stainless steel or other metals with surface coatings are preferably used if necessary. Filled plastics are also known, wherein, for example, thermosetting plastics or thermoplastics are provided as plastics. In particular, the corresponding ultrasonic reflector surface is manufactured by an additive manufacturing method. As a result, a highly accurate arrangement of the corresponding reflector surface on the carrier element is obtained. As a result, a one-piece construction together with the carrier element obtains particularly high precision when implementing quality determination.

Preferably, the ultrasonic reflector surfaces are arranged in such a way that the ultrasonic signal is reflected multiple times on at least one of the ultrasonic reflector surfaces. Multiple reflections can, for example, extend the propagation path of the ultrasonic signal in order to enable improved signal evaluation.

In addition, the device preferably has a controller, which is configured to control the inspection unit, in particular the ultrasonic transducer, and to generate and receive a burst signal as an ultrasonic signal so as to determine the mass concentration of the liquid based on the propagation time difference of the ultrasonic signal reflected from these ultrasonic reflector surfaces. The frequency range of the burst signal is preferably between 0.5 MHz and 10 MHz, preferably between 1 MHz and 2 MHz. Higher frequencies can achieve better spatial focusing of the ultrasonic field. And the transmission time can be determined more accurately. However, with increasing frequency, the absorption of the sound energy in the propagation medium also increases. The controller is also designed to evaluate the ultrasonic signal or echo received by the ultrasonic transducer to perform a quality determination. In particular, the controller is designed to determine the propagation time between the electrical excitation of the ultrasonic transducer, in particular the piezoelectric ceramic, and the received echo by means of a simple threshold value determination of the voltage amplitude of the received signal (echo) or by zero point detection or to determine the arrival of the maximum amplitude after determining the envelope or using a correlation method or other known methods for determining the propagation time from the time signal.

The tank device according to the invention is characterized by the design according to the invention of the device, which results in the advantages already mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS

In particular, further advantages and preferred features and feature combinations are obtained from the above-mentioned contents and from the preferred embodiments. Below, the present invention is explained in more detail with the aid of the accompanying drawings. For this purpose, in the accompanying drawings:

FIG1 shows a simplified side view of an advantageous tank arrangement;

FIG. 2 shows a simplified illustration of a first exemplary embodiment of an advantageous inspection unit of a tank device;

FIG3 shows a simplified diagram of a second embodiment of the inspection unit;

FIG4 shows a simplified diagram of a third embodiment of the inspection unit;

FIG5 shows a simplified diagram of a fourth embodiment of the inspection unit;

FIG6 shows a simplified diagram of a fifth embodiment of the inspection unit;

FIG7 shows a simplified diagram of a sixth embodiment of the inspection unit;

FIG8 shows a simplified diagram of a seventh embodiment of a checking unit; and

FIG. 9 shows a simplified illustration of an eighth exemplary embodiment of a checking unit.

Detailed ways

FIG. 1 shows a simplified diagram of an advantageous tank device 1 for an exhaust gas aftertreatment system of a motor vehicle. The tank device 1 has a tank 2 in which a liquid exhaust gas aftertreatment agent, in particular a reducing agent 3, is stored. An extraction module 4 is arranged in the tank 2, wherein the extraction module 4 is in particular located at the bottom of the tank 2. The extraction module carries a conveying device 5, by means of which the reducing agent can be sucked out of the tank 2 and conveyed to, for example, a metering valve or an injection valve by means of a pipeline 6. In addition, the extraction module 4 has in particular a filter connected upstream of the conveying device 5 and optionally a heating device in order to thaw frozen exhaust gas aftertreatment agents if necessary. The reducing agent is in particular a urea-water solution for producing ammonia, which interacts with the exhaust gas of the internal combustion engine of the motor vehicle in a manner that reduces nitrogen oxides. In order to determine the urea concentration in the liquid, there is a testing unit 7, which is also currently associated with the extraction module 4. Alternatively, the testing unit 7 is present independently in the tank 2. The testing unit 7 together with a controller 8 forms a device 9 for determining the quality of the liquid located in the tank 2 by determining the concentration.

2 to 9 , different exemplary embodiments of the test unit 7 are explained in more detail. These exemplary embodiments have in common that the test unit 7 each has an ultrasonic transducer and at least two ultrasonic reflector surfaces, wherein the ultrasonic reflector surfaces are arranged or formed on a one-piece carrier element.

2 shows a first exemplary embodiment of the inspection unit 7 in a simplified diagram. As described above, the inspection unit 7 has an ultrasonic transducer 10 which can be controlled by a control unit 8 and is designed as a piezoelectric ceramic ultrasonic transducer. Two ultrasonic reflector surfaces 11 and 12 are arranged opposite the ultrasonic transducer and are arranged on a common and integrally constructed carrier element 13.

In principle, it is known from the prior art to use ultrasonic transducers to determine fluid properties. Here, the measuring principle is based on the measurement of the propagation time in the liquid medium when the propagation path between the ultrasonic transducer and the receiver is known. Different medium properties can be obtained by the propagation speed of the sound signal in the fluid determined in this way and other measured variables sensed if necessary, such as the fluid temperature. Such ultrasonic transducers are used, for example, to determine and monitor the mass concentration of a urea-water solution located in a tank. The ultrasonic transducer converts an electrical signal into a sound wave and radiates the sound wave into the liquid or into the liquid located in the tank 2. The receiver converts the ultrasonic signal that reaches it and is sent by the ultrasonic transducer into an electrical signal that can be analyzed and evaluated afterwards. The known ultrasonic transducer is used not only as a transmitter but also as a receiver and uses the piezoelectric effect to convert between sound and electrical signals. In the so-called pulse echo operation, at least one reflector is required, which reflects the sound wave radiated by the ultrasonic transducer 10 back to the reflector through a known propagation path. Here, the vibration behavior and damping behavior of the ultrasonic transducer 10 can be taken into account. This results in a predetermined minimum length of the measuring path so that the mechanical vibrations generated by ultrasonic transducer 10 when transmitting an ultrasonic signal are damped to such an extent that when receiving the scattered echoes (reflected ultrasonic signals), a clear separation between the transmitted signal and the received signal is possible.

The advantageous embodiment of testing unit 7 shown in FIG. 2 results in a measuring distance ΔL which is not obtained from the distance between reflector surface and ultrasonic transducer 10 , but rather from the distance between reflector surfaces 11 , 12 from one another.

Two ultrasonic reflector surfaces 11, 12 are arranged opposite to the ultrasonic transducer 10. Here, the carrier element 13 is designed in a stepped shape, wherein the reflector surface 11 is located on the first level and the reflector surface 12 is located on the second level. Here, the second level is farther from the ultrasonic transducer 10 than the first level with the reflector surface 11. Therefore, different propagation paths _L1 and _L2 are obtained between the respective ultrasonic reflector surfaces 11, 12 and the ultrasonic transducer 10, and the difference between these two propagation paths results in a measuring section ΔL= _L2 - _L1 . Therefore, the measuring section is determined by the one-piece carrier element 13. Now, the propagation speed of the ultrasonic signal _cF is calculated from the propagation time difference Δt and the propagation path difference ΔL: _cF =ΔL/Δt.

Therefore, the absolute distance between the ultrasonic transducer 10 and the ultrasonic reflector surfaces 11, 12 is not included in the calculation and does not need to be known or constant. Since the carrier element 13 is constructed in one piece, thermal expansion hardly occurs or only occurs in a small amount in the set operating temperature range, and this thermal expansion has the same effect on the two ultrasonic reflector surfaces 11, 12. The propagation time difference of the two echoes or two reflected ultrasonic signals received by the ultrasonic transducer 10 is at least so large that the two ultrasonic signals are clearly separated from each other in time. Here, the longer propagation time difference caused by the longer propagation distance difference improves the accuracy of the medium characterization. In addition, more than two propagation paths can also be realized and therefore more than two echoes can be considered for analysis and evaluation, as explained in detail below.

According to the present embodiment of FIG. 2 , the reflectors 11 , 12 are designed as flat ultrasonic reflector surfaces 11 , 12 or as ultrasonic reflector surfaces 11 , 12 with flat/planar reflector surfaces. In order to achieve the highest possible signal amplitude of the reflected ultrasonic signal, a suitable reflector material is selected. In addition, by the curved shape of the reflector geometry of the individual ultrasonic reflector surfaces 11 , 12 , a focused reflection toward the ultrasonic transducer 11 can be achieved.

When selecting the reflector material, the acoustic impedance Z _R of each ultrasonic reflector surface 11, 12 is selected as high as possible. The acoustic impedance of the medium is obtained by the product of the specific density of the medium and the sound propagation speed in the medium. Under the assumption that a plane wave is incident from the liquid on the corresponding ultrasonic reflector 11, 12, the amplitude reflection coefficient R is obtained from the acoustic impedance Z _F of the liquid in the tank 2 and the corresponding ultrasonic reflector surface 11, 12, Z _R : R = (Z _R - _{Z F} ) / (Z _R + Z _F ).

A high backscattering is obtained for a given acoustic impedance Z _F of the fluid to be characterized when the impedance Z _R of the reflector is significantly greater than the impedance of the fluid: Z _R >> Z _F. Metals, ceramics or other materials with high acoustic impedance are particularly suitable as reflector materials. In the case of applications in corrosive liquids, stainless steel or other metals are particularly used, which can be protected by a surface coating if necessary. Other alternatives are filled plastics, such as thermosetting plastics or thermoplastics filled with metal or ceramic powders. The corresponding ultrasonic reflectors 11, 12 are preferably manufactured directly on the carrier element 13 by an additive manufacturing method.

FIG. 3 shows a second embodiment of the inspection unit 7, which differs from the previous embodiment in that the propagation time difference is increased due to multiple reflections. The difference from the previous embodiment is that the second reflector surface 12 is not oriented parallel to the ultrasonic transducer 10 and therefore also to the ultrasonic reflector surface 11, but is oriented obliquely, so that the ultrasonic signal is reflected back obliquely by the reflector surface 12. Here, a third reflector surface 14 is arranged on the carrier element 13, and the signal is reflected by the reflector surface 12 onto the third reflector surface, as shown by the dotted arrow. The ultrasonic reflector surface 14 is arranged in such a way that it reflects the reflected ultrasonic signal back to the ultrasonic transducer 10. As a result, the propagation time of the ultrasonic signal reflected by the ultrasonic reflector surface 12 is extended, and the measurement is optimized. At present, the third ultrasonic reflector surface 14 is also constructed as a planar reflector surface.

FIG. 4 shows a third embodiment of the test unit 7, which differs from the second embodiment in that a plurality of notches 15 are formed in the carrier element 13. The notches 15 are each formed in a reflector-free region of the carrier element 13 and serve, on the one hand, to reduce weight and, on the other hand, to minimize disturbing reflections on the surface of the carrier element, which are not part of the desired propagation path of the ultrasonic signal. In particular, only the surface of the carrier element that is necessary for reflection and mechanical stability is made of a material with a high acoustic impedance, while other regions of the carrier element are made of a material with a lower acoustic impedance, for example, of plastic. In particular, as described above, the carrier element as a whole is made of plastic, while the reflector surfaces 11, 12 and 14 are made of a material with a high impedance.

FIG. 5 shows a fourth embodiment of the inspection unit 7, which differs from the previous embodiment in that the multiply deflected propagation path has a longer path length. For this purpose, according to the embodiment of FIG. 5 , the first reflector 11 is arranged closer to the ultrasonic transducer 10. For this purpose, the reflector 11 is arranged on the front face (vorgesetzte ). In addition, the second ultrasonic reflector 12 in this embodiment is not configured as a plane, but as a curved surface, so as to achieve focused reflection of the ultrasonic signal toward the third ultrasonic reflector surface 14 and the ultrasonic transducer 10. For this purpose, the curved surface of the ultrasonic reflector 12 is particularly configured as a parabola, a spherical segment, or a cylindrical segment.

FIG6 shows a further embodiment of the inspection unit 7, which differs from the embodiment of FIG2 in particular in that the carrier element 13 is cylindrical overall, wherein the carrier element has a first section 16 with a diameter D1 and a second section 17 with a diameter D2, wherein the diameter D1 is significantly greater than the diameter D2, so that on the one hand the reflector 12 is obtained as an annular reflector surface on the section 16 and the reflector 11 is obtained on the end side of the section 17. This results in a rotationally symmetrical reflector component that can be realized cost-effectively and in a space-saving manner.

7 shows a sixth embodiment of the inspection unit 7, which differs from the embodiment of FIG. 5 in that multiple reflections occur on the reflector surface 12. For this purpose, the second reflector surface 12 and the third reflector surface 14 are arranged relative to each other in such a way that the ultrasonic signal reflected from the reflector surface 12 or deflected to the reflector surface 14 is deflected from the reflector surface 14 back to the reflector surface 12 and reflected from there back to the ultrasonic transducer 10. For this purpose, in particular, an angle α=45° formed by the planar reflector surfaces 12 and 14 is provided.

FIG8 shows a seventh embodiment of the inspection unit 7, which differs from the previous embodiment in that the second reflector 12 is arranged beside the ultrasonic transducer 10 and offset relative to the ultrasonic transducer in the propagation direction of the ultrasonic signal. In particular, the ultrasonic transducer 10 is located in the reflector 12, which therefore surrounds the ultrasonic transducer 10 on at least two sides. As mentioned above, the reflector surface 11 is opposite to the ultrasonic transducer 10, but has a surface that basically corresponds to the surface of the reflector surface 12. According to the current embodiment, the ultrasonic transducer 10 is configured to transmit dispersed ultrasonic waves, as shown by the solid line in FIG8. The transmitted ultrasonic signal arrives on the ultrasonic reflector surface 11, which itself has a curvature, which is selected so that the ultrasonic wave reflected by the curved surface is reflected back to the ultrasonic transducer 10 and the reflector surface 12 as a plane wave, as shown by the dashed line. These waves are sensed by the ultrasonic transducer 10 as first echoes. Since these waves also reach the ultrasonic reflector surface 12, they are reflected on the ultrasonic reflector back to the reflector surface 11, from where they are reflected back to the ultrasonic transducer 10 as second echoes.

FIG9 shows an eighth embodiment, which differs from the embodiment of FIG8 in that the ultrasonic transducer 10 is configured to transmit a planar ultrasonic signal or wave, as indicated by the solid line. The dispersed ultrasonic waves are reflected back by the curvature of the first reflector surface 11, and these dispersed ultrasonic waves not only reach the ultrasonic transducer 10 as the first echo, but also reach the second ultrasonic reflector surface 12, so as to be reflected back from there to the first reflector surface 11, which in turn reflects these waves back to the ultrasonic transducer 10 as the second echo. Here, the curvature of the reflector surface 11 is selected so that the divergent waves are reflected back in the direction of the ultrasonic transducer 10. Due to the beam broadening, a part of these waves also reaches the second reflector surface 12, which is also configured to be curved according to this embodiment, so that wave focusing occurs, and through this wave focusing, the ultrasonic signal is reflected back from the reflector surface 12 to the reflector surface 11 in a focused manner, so that these waves reach the curved reflector surface 11 again.

Claims (14)

1. A device (9) for determining the quality of a liquid, the device (9) comprising at least one inspection unit (7) which can be arranged in a tank (2) for storing the liquid, the inspection unit comprising: at least one ultrasonic transducer (10) for transmitting and receiving ultrasonic signals; and at least two ultrasonic reflector surfaces for reflecting the transmitted ultrasonic signals back to the at least one ultrasonic transducer (10), wherein the at least two ultrasonic reflector surfaces are directly constructed or arranged at different distances from the ultrasonic transducer (10) on a common and integrally constructed carrier element (13), wherein at least one of the at least two ultrasonic reflector surfaces is arranged next to the ultrasonic transducer (10) and offset relative to the ultrasonic transducer (10) in the propagation direction of the ultrasonic signal and opposite to another of the at least two ultrasonic reflector surfaces. 2 . The device ( 9 ) according to claim 1 , characterized in that at least two ultrasound reflector surfaces are designed to reflect ultrasound signals directly back to the ultrasonic transducer ( 10 ). 3 . 3 . The device ( 9 ) according to claim 1 , characterized in that at least one of the at least two ultrasound reflector surfaces is designed to deflect the ultrasound signal at least once before the ultrasound signal is reflected back to the ultrasound transducer ( 10 ). 4 . The device ( 9 ) according to claim 1 , characterized in that at least one of the at least two ultrasound reflector surfaces has a curvature. 5 . 5 . The device ( 9 ) according to claim 1 , characterized in that one and/or the other ultrasound reflector surface has a curved surface. 6 . The device ( 9 ) according to claim 1 , characterized in that the carrier element ( 13 ) has at least one recess ( 15 ) in a reflector-free region. 7 . The device ( 9 ) as claimed in claim 1 , characterized in that at least one of the at least two ultrasound reflector surfaces is designed as a coating on the carrier element ( 13 ). 8 . The device ( 9 ) according to claim 1 , characterized in that at least two ultrasound reflector surfaces are arranged in such a way that an ultrasound signal is reflected multiple times on at least one of the at least two ultrasound reflector surfaces. 9. The device (9) according to any one of claims 1 to 3 is characterized in that a controller (8) is provided, which is configured to control the inspection unit (7) to generate and receive at least one burst signal as an ultrasonic signal so as to determine the mass concentration in the liquid based on the propagation time difference of the ultrasonic signals reflected back by the at least two ultrasonic reflector surfaces. 10 . The device ( 9 ) according to claim 1 , characterized in that the liquid is an exhaust gas aftertreatment agent. 11 . The device ( 9 ) according to claim 9 , characterized in that the controller ( 8 ) is designed to control the ultrasonic transducer ( 10 ). 12. A tank device (1), comprising a tank (2) for storing and providing a liquid (3) and a device (9) for determining the quality of the liquid, wherein the device (9) for determining the quality of the liquid comprises at least one inspection unit (7) which can be arranged in the tank (2), characterized in that the device (9) is a device (9) according to any one of claims 1 to 11. 13. The tank device (1) according to claim 12, characterized in that the tank device (1) is a reducing agent tank device for an exhaust gas aftertreatment system of a motor vehicle. 14. Tank arrangement (1) according to claim 12 or 13, characterized in that the liquid (3) is an exhaust gas aftertreatment agent.